I have a TCL ADSL2+ connection in Auckland (presumably wholesaled from TNZ).  It syncs at 14Mbps down and I generally get local speed test results of 12Mbps.  Lately however it has been slowing down to under 1Mbps at various times of the day.  I've used testmy.net to run an hourly test and, although it is offshore and peaks at only 3Mbps, it clearly shows that my connection is being "managed".  The speed slowly tapers off to a crawl mid-morning and then jumps back to full speed right on midnight (see chart below).

I logged a question using TCL's online help and provided all the stats but, even though they promise a 48 hour response, I've only had one response in 16 days.  I phoned them this morning, the tech didn't know about any new speed throttling going on, and has asked me to perform isolation tests (unplug all phones, try a different modem, run speed tests) before they will run an analyser on my connection.  I guess I have to do these tests but I know what the result will be.  It's not my cabling or equipment that is slowing down my connection on a scheduled basis -- it's obviously something upstream.

Anyone else noticing this?  And does anyone have inside knowledge on what's changed recently?

Thanks - Simon